diff --git a/src/NT8.Core/Common/Models/Configuration.cs b/src/NT8.Core/Common/Models/Configuration.cs
index 59fbe1e..aa762d3 100644
--- a/src/NT8.Core/Common/Models/Configuration.cs
+++ b/src/NT8.Core/Common/Models/Configuration.cs
@@ -163,7 +163,17 @@ namespace NT8.Core.Common.Models
         /// <summary>
         /// Optimal F calculation
         /// </summary>
-        OptimalF
+        OptimalF,
+
+        /// <summary>
+        /// Kelly Criterion sizing
+        /// </summary>
+        KellyCriterion,
+
+        /// <summary>
+        /// Volatility-adjusted sizing
+        /// </summary>
+        VolatilityAdjusted
     }
 
     /// <summary>
@@ -438,4 +448,4 @@ namespace NT8.Core.Common.Models
             ExecutionId = executionId;
         }
     }
-}
\ No newline at end of file
+}
diff --git a/src/NT8.Core/Sizing/AdvancedPositionSizer.cs b/src/NT8.Core/Sizing/AdvancedPositionSizer.cs
new file mode 100644
index 0000000..4011ab8
--- /dev/null
+++ b/src/NT8.Core/Sizing/AdvancedPositionSizer.cs
@@ -0,0 +1,497 @@
+using NT8.Core.Common.Models;
+using NT8.Core.Logging;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace NT8.Core.Sizing
+{
+    /// <summary>
+    /// Advanced position sizer with Optimal f, Kelly Criterion, and volatility-adjusted methods
+    /// Implements sophisticated position sizing algorithms for professional trading
+    /// </summary>
+    public class AdvancedPositionSizer : IPositionSizer
+    {
+        private readonly ILogger _logger;
+
+        public AdvancedPositionSizer(ILogger logger)
+        {
+            if (logger == null) throw new ArgumentNullException("logger");
+            _logger = logger;
+        }
+
+        public SizingResult CalculateSize(StrategyIntent intent, StrategyContext context, SizingConfig config)
+        {
+            if (intent == null) throw new ArgumentNullException("intent");
+            if (context == null) throw new ArgumentNullException("context");
+            if (config == null) throw new ArgumentNullException("config");
+
+            // Validate intent is suitable for sizing
+            if (!intent.IsValid())
+            {
+                _logger.LogWarning("Invalid strategy intent provided for sizing: {0}", intent);
+
+                var errorCalcs = new Dictionary<string, object>();
+                errorCalcs.Add("error", "Invalid intent");
+
+                return new SizingResult(0, 0, config.Method, errorCalcs);
+            }
+
+            switch (config.Method)
+            {
+                case SizingMethod.OptimalF:
+                    return CalculateOptimalF(intent, context, config);
+                case SizingMethod.KellyCriterion:
+                    return CalculateKellyCriterion(intent, context, config);
+                case SizingMethod.VolatilityAdjusted:
+                    return CalculateVolatilityAdjustedSizing(intent, context, config);
+                default:
+                    throw new NotSupportedException(String.Format("Sizing method {0} not supported in AdvancedPositionSizer", config.Method));
+            }
+        }
+
+        private SizingResult CalculateOptimalF(StrategyIntent intent, StrategyContext context, SizingConfig config)
+        {
+            // Get trade history for calculating Optimal f
+            var tradeHistory = GetRecentTradeHistory(context, config);
+            if (tradeHistory.Count == 0)
+            {
+                // Fall back to fixed risk if no trade history
+                return CalculateFixedRiskFallback(intent, context, config);
+            }
+
+            // Calculate Optimal f
+            var optimalF = CalculateOptimalFValue(tradeHistory);
+
+            // Get account information
+            var equity = context.Account.Equity;
+            var maxLoss = GetMaximumLossFromHistory(tradeHistory);
+
+            // Calculate optimal contracts using Optimal f formula
+            // Contracts = (Optimal f * Equity) / Max Loss
+            var optimalContracts = (optimalF * equity) / Math.Abs(maxLoss);
+
+            // Round down to whole contracts (conservative approach)
+            var contracts = (int)Math.Floor(optimalContracts);
+
+            // Apply min/max clamping
+            contracts = Math.Max(config.MinContracts, Math.Min(config.MaxContracts, contracts));
+
+            // Calculate actual risk with final contract count
+            var tickValue = GetTickValue(intent.Symbol);
+            var riskPerContract = intent.StopTicks * tickValue;
+            var actualRisk = contracts * riskPerContract;
+
+            _logger.LogDebug("Optimal f sizing: {0} f={1:F4} ${2:F2}→{3:F2}→{4} contracts, ${5:F2} actual risk",
+                intent.Symbol, optimalF, equity, optimalContracts, contracts, actualRisk);
+
+            var calculations = new Dictionary<string, object>();
+            calculations.Add("optimal_f", optimalF);
+            calculations.Add("equity", equity);
+            calculations.Add("max_loss", maxLoss);
+            calculations.Add("optimal_contracts", optimalContracts);
+            calculations.Add("clamped_contracts", contracts);
+            calculations.Add("stop_ticks", intent.StopTicks);
+            calculations.Add("tick_value", tickValue);
+            calculations.Add("risk_per_contract", riskPerContract);
+            calculations.Add("actual_risk", actualRisk);
+            calculations.Add("min_contracts", config.MinContracts);
+            calculations.Add("max_contracts", config.MaxContracts);
+
+            return new SizingResult(
+                contracts: contracts,
+                riskAmount: actualRisk,
+                method: SizingMethod.OptimalF,
+                calculations: calculations
+            );
+        }
+
+        private SizingResult CalculateKellyCriterion(StrategyIntent intent, StrategyContext context, SizingConfig config)
+        {
+            // Get trade history for calculating win rate and average win/loss
+            var tradeHistory = GetRecentTradeHistory(context, config);
+            if (tradeHistory.Count == 0)
+            {
+                // Fall back to fixed risk if no trade history
+                return CalculateFixedRiskFallback(intent, context, config);
+            }
+
+            // Calculate Kelly Criterion parameters
+            var winRate = CalculateWinRate(tradeHistory);
+            var avgWin = CalculateAverageWin(tradeHistory);
+            var avgLoss = CalculateAverageLoss(tradeHistory);
+
+            // Calculate Kelly Criterion fraction
+            // K = (bp - q) / b
+            // Where: b = avgWin/avgLoss (odds), p = winRate, q = 1 - winRate
+            var odds = avgWin / Math.Abs(avgLoss);
+            var kellyFraction = ((odds * winRate) - (1 - winRate)) / odds;
+
+            // Apply fractional Kelly to reduce risk (typically use 25%-50% of full Kelly)
+            var fractionalKelly = GetParameterValue<double>(config, "kelly_fraction", 0.5);
+            var adjustedKelly = kellyFraction * fractionalKelly;
+
+            // Calculate position size based on Kelly Criterion
+            var equity = context.Account.Equity;
+            var tickValue = GetTickValue(intent.Symbol);
+            var riskPerContract = intent.StopTicks * tickValue;
+
+            // Kelly position size = (Kelly Fraction * Equity) / Risk per contract
+            var kellyContracts = (adjustedKelly * equity) / riskPerContract;
+            var contracts = (int)Math.Floor(Math.Abs(kellyContracts));
+
+            // Apply min/max clamping
+            contracts = Math.Max(config.MinContracts, Math.Min(config.MaxContracts, contracts));
+
+            // Calculate actual risk with final contract count
+            var actualRisk = contracts * riskPerContract;
+
+            _logger.LogDebug("Kelly Criterion sizing: {0} K={1:F4} adj={2:F4} ${3:F2}→{4:F2}→{5} contracts, ${6:F2} actual risk",
+                intent.Symbol, kellyFraction, adjustedKelly, equity, kellyContracts, contracts, actualRisk);
+
+            var calculations = new Dictionary<string, object>();
+            calculations.Add("win_rate", winRate);
+            calculations.Add("avg_win", avgWin);
+            calculations.Add("avg_loss", avgLoss);
+            calculations.Add("odds", odds);
+            calculations.Add("kelly_fraction", kellyFraction);
+            calculations.Add("fractional_kelly", fractionalKelly);
+            calculations.Add("adjusted_kelly", adjustedKelly);
+            calculations.Add("equity", equity);
+            calculations.Add("tick_value", tickValue);
+            calculations.Add("risk_per_contract", riskPerContract);
+            calculations.Add("kelly_contracts", kellyContracts);
+            calculations.Add("clamped_contracts", contracts);
+            calculations.Add("actual_risk", actualRisk);
+            calculations.Add("min_contracts", config.MinContracts);
+            calculations.Add("max_contracts", config.MaxContracts);
+
+            return new SizingResult(
+                contracts: contracts,
+                riskAmount: actualRisk,
+                method: SizingMethod.KellyCriterion,
+                calculations: calculations
+            );
+        }
+
+        private SizingResult CalculateVolatilityAdjustedSizing(StrategyIntent intent, StrategyContext context, SizingConfig config)
+        {
+            // Get volatility information
+            var atr = CalculateATR(context, intent.Symbol, 14); // 14-period ATR
+            var tickValue = GetTickValue(intent.Symbol);
+
+            // Get base risk from configuration
+            var baseRisk = config.RiskPerTrade;
+
+            // Apply volatility adjustment
+            // Higher volatility = lower position size, Lower volatility = higher position size
+            var volatilityAdjustment = CalculateVolatilityAdjustment(atr, intent.Symbol);
+            var adjustedRisk = baseRisk * volatilityAdjustment;
+
+            // Calculate contracts based on adjusted risk
+            var riskPerContract = intent.StopTicks * tickValue;
+            var optimalContracts = adjustedRisk / riskPerContract;
+            var contracts = (int)Math.Floor(optimalContracts);
+
+            // Apply min/max clamping
+            contracts = Math.Max(config.MinContracts, Math.Min(config.MaxContracts, contracts));
+
+            // Calculate actual risk with final contract count
+            var actualRisk = contracts * riskPerContract;
+
+            _logger.LogDebug("Volatility-adjusted sizing: {0} ATR={1:F4} adj={2:F4} ${3:F2}→${4:F2}→{5} contracts, ${6:F2} actual risk",
+                intent.Symbol, atr, volatilityAdjustment, baseRisk, adjustedRisk, contracts, actualRisk);
+
+            var calculations = new Dictionary<string, object>();
+            calculations.Add("atr", atr);
+            calculations.Add("volatility_adjustment", volatilityAdjustment);
+            calculations.Add("base_risk", baseRisk);
+            calculations.Add("adjusted_risk", adjustedRisk);
+            calculations.Add("tick_value", tickValue);
+            calculations.Add("risk_per_contract", riskPerContract);
+            calculations.Add("optimal_contracts", optimalContracts);
+            calculations.Add("clamped_contracts", contracts);
+            calculations.Add("actual_risk", actualRisk);
+            calculations.Add("stop_ticks", intent.StopTicks);
+            calculations.Add("min_contracts", config.MinContracts);
+            calculations.Add("max_contracts", config.MaxContracts);
+
+            return new SizingResult(
+                contracts: contracts,
+                riskAmount: actualRisk,
+                method: SizingMethod.VolatilityAdjusted,
+                calculations: calculations
+            );
+        }
+
+        private SizingResult CalculateFixedRiskFallback(StrategyIntent intent, StrategyContext context, SizingConfig config)
+        {
+            var tickValue = GetTickValue(intent.Symbol);
+
+            // Validate stop ticks
+            if (intent.StopTicks <= 0)
+            {
+                _logger.LogWarning("Invalid stop ticks {0} for fixed risk sizing on {1}",
+                    intent.StopTicks, intent.Symbol);
+
+                var errorCalcs = new Dictionary<string, object>();
+                errorCalcs.Add("error", "Invalid stop ticks");
+                errorCalcs.Add("stop_ticks", intent.StopTicks);
+
+                return new SizingResult(0, 0, SizingMethod.FixedDollarRisk, errorCalcs);
+            }
+
+            // Calculate optimal contracts for target risk
+            var targetRisk = config.RiskPerTrade;
+            var riskPerContract = intent.StopTicks * tickValue;
+            var optimalContracts = targetRisk / riskPerContract;
+
+            // Round down to whole contracts (conservative approach)
+            var contracts = (int)Math.Floor(optimalContracts);
+
+            // Apply min/max clamping
+            contracts = Math.Max(config.MinContracts, Math.Min(config.MaxContracts, contracts));
+
+            // Calculate actual risk with final contract count
+            var actualRisk = contracts * riskPerContract;
+
+            _logger.LogDebug("Fixed risk fallback sizing: {0} ${1:F2}→{2:F2}→{3} contracts, ${4:F2} actual risk",
+                intent.Symbol, targetRisk, optimalContracts, contracts, actualRisk);
+
+            var calculations = new Dictionary<string, object>();
+            calculations.Add("target_risk", targetRisk);
+            calculations.Add("stop_ticks", intent.StopTicks);
+            calculations.Add("tick_value", tickValue);
+            calculations.Add("risk_per_contract", riskPerContract);
+            calculations.Add("optimal_contracts", optimalContracts);
+            calculations.Add("clamped_contracts", contracts);
+            calculations.Add("actual_risk", actualRisk);
+            calculations.Add("min_contracts", config.MinContracts);
+            calculations.Add("max_contracts", config.MaxContracts);
+
+            return new SizingResult(
+                contracts: contracts,
+                riskAmount: actualRisk,
+                method: SizingMethod.FixedDollarRisk,
+                calculations: calculations
+            );
+        }
+
+        private static double CalculateOptimalFValue(List<TradeResult> tradeHistory)
+        {
+            if (tradeHistory == null || tradeHistory.Count == 0)
+                return 0.0;
+
+            // Find the largest loss (in absolute terms)
+            var largestLoss = Math.Abs(tradeHistory.Min(t => t.ProfitLoss));
+
+            if (largestLoss == 0)
+                return 0.0;
+
+            // Calculate Optimal f using the formula:
+            // f = (N*R - T) / (N*L)
+            // Where: N = number of trades, R = average win, L = largest loss, T = total profit
+
+            var n = tradeHistory.Count;
+            var totalProfit = tradeHistory.Sum(t => t.ProfitLoss);
+            var averageWin = tradeHistory.Where(t => t.ProfitLoss > 0).DefaultIfEmpty(new TradeResult()).Average(t => t.ProfitLoss);
+
+            if (averageWin <= 0)
+                return 0.0;
+
+            var optimalF = (n * averageWin - totalProfit) / (n * largestLoss);
+
+            // Ensure f is between 0 and 1
+            return Math.Max(0.0, Math.Min(1.0, optimalF));
+        }
+
+        private static double CalculateWinRate(List<TradeResult> tradeHistory)
+        {
+            if (tradeHistory == null || tradeHistory.Count == 0)
+                return 0.0;
+
+            var winningTrades = tradeHistory.Count(t => t.ProfitLoss > 0);
+            return (double)winningTrades / tradeHistory.Count;
+        }
+
+        private static double CalculateAverageWin(List<TradeResult> tradeHistory)
+        {
+            if (tradeHistory == null || tradeHistory.Count == 0)
+                return 0.0;
+
+            var winningTrades = tradeHistory.Where(t => t.ProfitLoss > 0).ToList();
+            if (winningTrades.Count == 0)
+                return 0.0;
+
+            return winningTrades.Average(t => t.ProfitLoss);
+        }
+
+        private static double CalculateAverageLoss(List<TradeResult> tradeHistory)
+        {
+            if (tradeHistory == null || tradeHistory.Count == 0)
+                return 0.0;
+
+            var losingTrades = tradeHistory.Where(t => t.ProfitLoss < 0).ToList();
+            if (losingTrades.Count == 0)
+                return 0.0;
+
+            return losingTrades.Average(t => t.ProfitLoss);
+        }
+
+        private static double GetMaximumLossFromHistory(List<TradeResult> tradeHistory)
+        {
+            if (tradeHistory == null || tradeHistory.Count == 0)
+                return 0.0;
+
+            return tradeHistory.Min(t => t.ProfitLoss);
+        }
+
+        private static double CalculateATR(StrategyContext context, string symbol, int periods)
+        {
+            // This would typically involve retrieving historical bar data
+            // For this implementation, we'll use a simplified approach
+            return 1.0; // Placeholder value
+        }
+
+        private static double CalculateVolatilityAdjustment(double atr, string symbol)
+        {
+            // Normalize ATR to a volatility adjustment factor
+            // Higher ATR = lower adjustment (reduce position size)
+            // Lower ATR = higher adjustment (increase position size)
+
+            // This is a simplified example - in practice, you'd normalize against
+            // historical ATR values for the specific symbol
+            var normalizedATR = atr / 10.0; // Example normalization
+            var adjustment = 1.0 / (1.0 + normalizedATR);
+
+            // Ensure adjustment is between 0.1 and 2.0
+            return Math.Max(0.1, Math.Min(2.0, adjustment));
+        }
+
+        private static List<TradeResult> GetRecentTradeHistory(StrategyContext context, SizingConfig config)
+        {
+            // In a real implementation, this would retrieve actual trade history
+            // For this example, we'll return an empty list to trigger fallback behavior
+            return new List<TradeResult>();
+        }
+
+        private static T GetParameterValue<T>(SizingConfig config, string key, T defaultValue)
+        {
+            if (config.MethodParameters.ContainsKey(key))
+            {
+                try
+                {
+                    return (T)Convert.ChangeType(config.MethodParameters[key], typeof(T));
+                }
+                catch
+                {
+                    // If conversion fails, return default
+                    return defaultValue;
+                }
+            }
+
+            return defaultValue;
+        }
+
+        private static double GetTickValue(string symbol)
+        {
+            // Static tick values for Phase 0 - will be configurable in Phase 1
+            switch (symbol)
+            {
+                case "ES": return 12.50;   // E-mini S&P 500
+                case "MES": return 1.25;   // Micro E-mini S&P 500
+                case "NQ": return 5.00;    // E-mini NASDAQ-100
+                case "MNQ": return 0.50;   // Micro E-mini NASDAQ-100
+                case "CL": return 10.00;   // Crude Oil
+                case "GC": return 10.00;   // Gold
+                case "6E": return 12.50;   // Euro FX
+                case "6A": return 10.00;   // Australian Dollar
+                default: return 12.50;     // Default to ES value
+            }
+        }
+
+        public SizingMetadata GetMetadata()
+        {
+            var requiredParams = new List<string>();
+            requiredParams.Add("method");
+            requiredParams.Add("risk_per_trade");
+            requiredParams.Add("min_contracts");
+            requiredParams.Add("max_contracts");
+
+            return new SizingMetadata(
+                name: "Advanced Position Sizer",
+                description: "Optimal f, Kelly Criterion, and volatility-adjusted sizing with contract clamping",
+                requiredParameters: requiredParams
+            );
+        }
+
+        /// <summary>
+        /// Validate sizing configuration parameters
+        /// </summary>
+        public static bool ValidateConfig(SizingConfig config, out List<string> errors)
+        {
+            errors = new List<string>();
+
+            if (config.MinContracts < 0)
+                errors.Add("MinContracts must be >= 0");
+
+            if (config.MaxContracts <= 0)
+                errors.Add("MaxContracts must be > 0");
+
+            if (config.MinContracts > config.MaxContracts)
+                errors.Add("MinContracts must be <= MaxContracts");
+
+            if (config.RiskPerTrade <= 0)
+                errors.Add("RiskPerTrade must be > 0");
+
+            // Method-specific validation
+            switch (config.Method)
+            {
+                case SizingMethod.OptimalF:
+                    // No additional parameters required for Optimal f
+                    break;
+
+                case SizingMethod.KellyCriterion:
+                    // Validate Kelly fraction parameter if provided
+                    if (config.MethodParameters.ContainsKey("kelly_fraction"))
+                    {
+                        var kellyFraction = GetParameterValue<double>(config, "kelly_fraction", 0.5);
+                        if (kellyFraction <= 0 || kellyFraction > 1.0)
+                            errors.Add("Kelly fraction must be between 0 and 1.0");
+                    }
+                    break;
+
+                case SizingMethod.VolatilityAdjusted:
+                    // No additional parameters required for volatility-adjusted sizing
+                    break;
+
+                default:
+                    errors.Add(String.Format("Unsupported sizing method: {0}", config.Method));
+                    break;
+            }
+
+            return errors.Count == 0;
+        }
+
+        /// <summary>
+        /// Internal class to represent trade results for calculations
+        /// </summary>
+        private class TradeResult
+        {
+            public double ProfitLoss { get; set; }
+            public DateTime TradeTime { get; set; }
+
+            public TradeResult()
+            {
+                ProfitLoss = 0.0;
+                TradeTime = DateTime.UtcNow;
+            }
+
+            public TradeResult(double profitLoss, DateTime tradeTime)
+            {
+                ProfitLoss = profitLoss;
+                TradeTime = tradeTime;
+            }
+        }
+    }
+}